This invention relates generally to wind turbines, and more particularly to a system for protecting the wind turbine during shut down or emergency stop.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is then fed into a utility grid.
Wind turbines require redundant braking systems in order to satisfy safety requirements. A first brake system conventionally uses aerodynamic braking to pitch the turbine blades into a feathered position and includes a stored energy source so that blade pitch can occur after a loss of power in a utility grid. A second brake system conventionally includes a disk brake not capable of stopping a turbine against full wind torque. Blade pitch has been accomplished on commercial wind turbines with a hydraulic ram and rotating coupling arrangement that can be readily backed up with a hydraulic accumulator, or an electrical DC system with a battery backup and DC motors. A third brake solution is the movement of the blades out of the wind by yaw activation (e.g., 90°. However, all of these known braking systems have been known to fail, and catastrophic damage, in some cases, has occurred to the wind turbine.